1. Field of the Invention
The field relates to a device and a method for optical recording and a signal processing circuit, and more particularly, to a device and a method for optical recording and a signal processing circuit in which a recording condition can be optimized depending on the compatibility between a drive and a medium.
2. Description of the Related Technology
In a recording onto optical information recording media such as CD-R or DVD-R (hereinafter referred to as “media” or a “medium”), the compatibility between a medium to be recorded on and a device to be used for recording (hereinafter referred to as a “drive”) depends on each combination of them. This may be caused by the medium side factor wherein an optimum recording condition is varied by the difference in a recording material comprising the medium or the film formation variation during production, or by the drive side factor wherein an optimum recording condition is varied by the difference in a pickup device and/or a semiconductor laser comprising the drive or assembly variation during production. In fact, a suitable recording condition exists for each combination of a medium and a drive due to the combination of those factors.
Accordingly, in a conventional method, ID information of a medium type identifiable by a drive is stored in the medium as well as a recording condition prepared for each medium type is stored in the drive. When a recording is actually conducted, the ID information stored in the medium is read from the medium loaded to the drive, and a recording condition related to the ID information (hereinafter referred to as a “writing strategy”) is used.
However, in the conventional method, suitable recording conditions can be selected for pre-verified known media, but prepared recording conditions may not be adequate to accommodate unknown media that are not pre-verified. Further, depending on the changes in recording environments such as a recording speed, disturbance, and change over time, the prepared recording conditions may not be adequate even for known media.
A method contemplated to accommodate such an unknown medium is described in Japanese Unexamined Patent Publication Nos. 2003-30837 and 2004-110995. As described in the paragraph [0020] of the Japanese Unexamined Patent Publication No. 2003-30837 as “. . . a phase error relative to a channel clock is detected for every recording pattern. A recording compensation parameter adjustment section 12 optimizes an emission waveform rule on the basis of a result of the detection at the phase error detection section 11”, a method for detecting a phase error by comparing with a channel clock and of correcting the phase error is disclosed.
Also, the paragraph [0024] of Japanese Unexamined Patent Publication No. 2003-30837 describes that “Next, a test pattern for determining an emission waveform rule is recorded. The area onto which the test pattern is recorded is reproduced, and the relationship between a prepared emission waveform rule and a phase error amount is examined. In other words, the phase error amount in the combination of the length of each mark and the length of each space immediately before the mark is measured. An emission waveform rule wherein the phase error amount becomes zero is estimated from the measured phase error amount, whereby a desired emission waveform rule is determined . . . ”, disclosing a method for measuring a phase error amount for every combination of a mark and a space, and then estimating an emission waveform rule wherein the phase error amount becomes zero (see FIG. 8 and FIG. 12).
The method disclosed in Japanese Unexamined Patent Publication No. 2003-30837 is effective for optimizing a strategy because correction is made based on a phase error of a recording pattern.
However, because the method disclosed in Japanese Unexamined Patent Publication No. 2003-30837 involves, as conventional methods, a fine adjustment of a prepared strategy stored in a drive, it is difficult to provide favorable recording quality for media to which prepared strategies are not applicable.
Also, the paragraph [0045] of Japanese Unexamined Patent Publication No. 2004-110995 describes that “. . . a top pulse correspondingly to a 3T period and a non-multipulse correspondingly to a 8T period are generated integrally (consecutively) . . . ” and the paragraph [0046] of the document describes that “. . . the laser power for a write pulse is adjusted in two levels, and when the ratio between a laser power (a height value of the top pulse) Ph and a laser power (a height value of the non-multipulse) Pm is optimum, an optimum power can be obtained . . . ”, suggesting the effectiveness of optimizing the Ph/Pm ratio.
However, in the method disclosed in Japanese Unexamined Patent Publication No. 2004-110995, as described in the paragraph [0067] of the document, initial values of Ph and Pm are temporarily set based on values stored in a drive or a medium, and then the Ph/Pm ratio is calculated. Accordingly, as in the case of Japanese Unexamined Patent Publication No. 2003-30837, it is difficult to provide favorable recording quality for media to which the temporarily set values are not applicable.
On the other hand, in the case of recording data onto a certain recording medium with an optical information recording system, generally, a recording condition suitable for the recording medium is obtained by a test recording using a test area provided on the recording medium prior to an actual data recording.
However, in an optical information recording system to which a high-speed recording is increasingly demanded, the positional relation between the test recording area and an actual recording area and the limited rotation number of a spindle motor that rotates the recording medium make a test recording difficult at the same speed as that used for an actual recording.
Therefore, a conventional method is generally used, wherein a recording condition suitable for each recording speed is pre-stored for each type of media in a recording apparatus that conducts a data recording, and when the high-speed recording is actually conducted, reading out and configuring the recording condition allow the data recording to be conducted.
The conventional method includes a step wherein a recording condition for a high-speed recording is slightly adjusted using the difference between an optimum recording condition obtained by a test recording conducted at a recording speed available for the test recording and that pre-stored in the recording apparatus.
However, this type of conventional method cannot adequately accommodate the variations in characteristics of a recording medium or a recording system. Further, there also exists a problem that it cannot adequately accommodate “unknown media” that are recording media on which information is not pre-stored in the recording apparatus or which is developed after the manufacture of the recording apparatus. Accordingly, there is a demand for a technology to obtain an optimum recording condition for each recording speed, depending on the characteristic of a medium or recording apparatus used for data recording.
To solve the above-described problem, a method wherein the relationship between amplitude information and a recording power at two or more recording speeds, which is pre-stored in the recording medium, is read out to calculate a recording power at a recording speed to be used for recording is disclosed in Japanese Unexamined Patent Publication No. 2004-234698. However, because the above-described method assumes that information for calculating a recording power is pre-stored in a recording medium, there persist three problems that the method: 1) cannot accommodate media on which the information is not pre-stored, 2) causes the decrease in productivity and the increase in cost at a manufacturing stage due to an additional production process for recording the information onto media, and 3) does not adequately accommodate the case where a system has a difficulty in recording with the calculated recording power.
Further, in a recording system such as CAV or CLV in which a recording speed is varied from an inner to outer circumference, an optimum recording condition is shifted due to various factors such as the change in temperature of a drive during recording and the difference in characteristics of a medium between inner and outer circumferences in addition to the change in an optimum recording condition caused by the variation in recording speed.
A method for adjusting such shifts is described in Japanese Unexamined Patent Publication No. 2002-208139. Japanese Unexamined Patent Publication No. 2002-208139 discloses a method comprising: sectioning an optical disk medium in a radial direction into a plurality of recording areas; reproducing an end part recorded on, for each of the recording areas; and correcting a power using characteristics of a resultant reproduction signal.
However, although Japanese Unexamined Patent Publication No. 2002-208139 describes the method for correcting a power in detail, any specific method for correcting a pulse width is not disclosed. Accordingly, a precise correction of a pulse width is not easy even if a known method for correcting a pulse width is simply applied to the method disclosed in Japanese Unexamined Patent Publication No. 2002-208139.
It is therefore an object of certain inventive aspects to provide a method for optimizing a recording condition depending on the compatibility between a drive and a medium. More particularly, certain inventive aspects provide a method effective to obtain a preferable recording condition even for high-speed recordings in which conducting a test recording is not easy, and further, a method effective for configuring an optimum recording condition for CAV or CLV recording in which a recording speed is varied from an inner to outer circumference.